External frame backpacks are particularly well suited for carrying heavy, bulky loads by backpackers. The load is carried a small distance away from the back of the user and is secured to a rigid frame that can transmit the load primarily to the hipbelt. However, with conventional frames and hipbelts, the load is not effectively transferred to the sides of the hips, the location most comfortable over a long haul. Instead the load is mainly carried by the small of the back as the hipbelt sags and pulls from behind.
Some attempts at overcoming this loading have been made by the use of straps and other equipment. For example, one attempted solution employs T-shaped arms rigidly secured to the frame rails and extending forwardly to an attachment with the sides of the hipbelt. This arrangement will transfer the load to the sides of the user's hips, but may also cause the pack to shift or swing side to side with every natural hip movement of the user. The connection is kept somewhat rigid for effective transfer of the load to the user's hips.
Other problems with external frame pack harnesses involve the back and lower panels that are used to suspend the pack frame away from direct contact with the user's back. These panels are strapped to the side rails of the pack and held in tension horizontally. They may, therefore, develop horizontal wrinkles or folds that are uncomfortable on the back of the user. Furthermore, the load may not be effectively and evenly distributed across these panels for a comfortable carry.
Owing to the limitation of the current external frame packs, the advantages of these packs being effective big-load haulers is overshadowed. A need therefore exists for a rigid external frame pack with a flexible harness system that effectively carries a load comfortably on the back with the bulk of the downward force being transferred to the sides of the hips of the user without pack instabilities being created when hiking.